Absolute multi-revolution encoder

ABSTRACT

Magnetic field detection elements and detect a magnetic material member formed at a rotary disc. An A pulse generation portion and a B pulse generation portion generate an A pulse a and a B pulse b which phases differ by 90 degrees to each other. The B pulse generation portion is supplied with the power from a backup power supply for a predetermined time period necessary for detecting the level of the B pulse from a time point of the edge of the A pulse.

TECHNICAL FIELD

The present invention relates a multi-revolution detection circuit foran encoder which detects the multi-revolution amount of a rotary memberand, in particular, relates to an absolute multi-revolution encoderrealizing the power saving.

RELATED ART

The absolute multi-revolution encoder is required to maintain thecounting state of a multi-revolution amount and to always detect andstore the multi-revolution amount even if power is not supplied from anexternal power supply. A backup power supply, for supplying power to acircuit when not supplied from the external power supply, is required toreduce a consumption current as small as possible thereby to elongatethe life time of the backup power supply.

To this end, for example, there has been employed a method in which apower to be supplied to an element used for a detection circuit, inparticular, an LED having a large consumption current is fed in apulsation manner at the time of operating a backup power supply therebyto reduce a consumption current.

FIG. 10 is a side view showing the mechanical configuration of anabsolute multi-revolution encoder of a related art. In the figure, areference numeral 50 depicts a rotary disc and 51 an optical slitpattern formed at the rotary disc 50. Further, a reference numeral 70depicts an LED, 71 a lens and 72 a light receiving element. These threeelements constitute an optical detecting means for detecting rotationpositional information from the optical slit pattern 51. A referencenumeral 60 depicts another rotary disc, 61 a magnetic material memberformed on the rotary disc, and 62 a magnetoresistive element fordetecting the magnetic material member 61.

FIG. 11 is a plan view showing the configuration of the rotary discs 50and 60. The magnetic material member 61 is provided over a predeterminedangular range near an origin including the origin position of theoptical slit pattern 51 formed at the rotary disc 50.

Next, the operation will be explained.

When the power is supplied from the external power supply, the LED 70 iscontinuously fed and the optical detecting means including the LED 70detects a position within one revolution from the optical slit pattern51 formed at the rotary disc 50 thereby to update a not-shown counter atthe origin position to detect a multi-revolution amount. Upon the backupoperation where the external power supply is cut off and power issupplied from the backup power supply, the magnetoresistive element 62detects the magnetic material member 61 formed at the rotary disc 60when passing the origin, whereby the LED 70 is fed by the backup powersupply for a predetermined time period determined by a rising edge and afalling edge respectively corresponding to the end portions of themagnetic material member 61 of an origin near signal generated by anot-shown circuit. It is determined, from a rotation position detectionsignal obtained when the LED 70 is fed, whether or not the rotary discpasses the origin position and also determining the rotation directionwhen it is determined that the rotary disc passes the origin position.

In this manner, upon the backup operation, the LED is fed by the backuppower supply for the predetermined time period necessary fordetermining, from the rotation position detection signal, whether or notthe rotary disc passes the origin position and also determining therotation direction when it is determined that the rotary disc passes theorigin position, whereby the reduction of the consumption current andthe elongation of the life time of the backup power supply are intended(see patent document 1, for example).

Patent Document 1: JP-A-5-79853

DISCLOSURE OF THE INVENTION

Problems to be Solved by the Invention

The absolute multi-revolution encoder of the related art requires tofeed power to the LED having a large consumption current even for ashort time in order to detect a multi-revolution amount. Thus, there isa limit to reduce the consumption current, which is a large obstacle torealize the elongation of the life time of the backup power supply.

The invention is made in view of the aforesaid problem of the relatedart and an object of the invention is to provide an absolutemulti-revolution encoder which can realize to largely elongate the lifetime of a backup power supply.

Means for Solving the Problems

In order to solve the aforesaid problem, the invention is configured inthe following manner.

According to claim 1, there is provided with an absolutemulti-revolution encoder including:

a rotary disc;

a multi-revolution signal generation portion; and

a within-one-revolution signal generation portion, wherein

the rotary disc includes a magnetic material member which generates amulti-revolution signal, and

the multi-revolution signal generation portion includes:

-   -   an A-phase magnetic field detection element and a B-phase        magnetic field detection element which detect leakage fluxes of        the magnetic material member and output signals of one        pulse/revolution having phases different by 90 degrees        therebetween,    -   an A-pulse generation portion including an A-phase detection        portion which detects a signal from the A-phase magnetic field        detection element and an A-pulse generation circuit which        converts the detected signal into an A pulse of a rectangular        wave shape,    -   a B-pulse generation portion including a B-phase detection        portion which detects a signal from the B-phase magnetic field        detection element and an B-pulse generation circuit-which        converts the detected-signal into a B pulse of a rectangular        wave shape,    -   a counter which counts the A pulse and the B pulse to generate        the multi-revolution signal, and    -   a power supply means which supplies power from a backup power        supply for a predetermine time period to at least one of the        B-phase detection portion and the B-pulse generation circuit        based on the A pulse or to at least one of the A-phase detection        portion and the A-pulse generation circuit based on the B pulse.

According to claim 2, it is characterized in that

at least one of the A-phase magnetic field detection element and theB-phase magnetic field detection element is an MR element.

According to claim 3, there is provided with an absolutemulti-revolution encoder including:

a rotary disc;

a multi-revolution signal generation portion; and

a within-one-revolution signal generation portion, wherein

the rotary disc includes a magnetic material member which generates amulti-revolution signal,

the magnetic material member is formed of a permanent magnetic which ismagnetized along a direction perpendicular to a rotation axis of therotary disc, and

the multi-revolution signal generation portion includes:

-   -   an A-phase magnetic field detection element and a B-phase        magnetic field detection element which detect leakage fluxes of        the magnetic material member and output signals of one        pulse/revolution having phases different by 90 degrees        therebetween,    -   an A-pulse generation portion including an A-phase detection        portion which detects a signal from the A-phase magnetic field        detection element and an A-pulse generation circuit which        converts the detected signal into an A pulse of a rectangular        wave shape,    -   a B-pulse generation portion including a B-phase detection        portion which detects a signal from the B-phase magnetic field        detection element and an B-pulse generation circuit which        converts the detected signal into a B pulse of a rectangular        wave shape,    -   a counter which counts the A pulse and the B pulse to generate        the multi-revolution signal,    -   a T-phase magnetic field detection element which detects leakage        fluxes of the magnetic material member and outputs a signal of        two pulses/revolution,    -   a T-pulse generation portion including a T-phase detection        portion which detects a signal from the T-phase magnetic field        detection element and a T-pulse generation circuit which        converts the detected signal into a T pulse of a rectangular        wave shape, and    -   a power supply means which supplies power from a backup power        supply for a predetermine time period to either one of the        A-phase detection portion, the B-phase detection portion and the        A-pulse generation circuit, the B-pulse generation circuit based        on the T pulse.

According to claim 4, it is characterized in that

each of the A-phase magnetic field detection element and the B-phasemagnetic field detection element is a Hall element, and

the T-phase magnetic field detection element is an MR element.

According to claim 5, it is characterized in that

a circuit board is disposed in parallel to the rotary disc via a gap,

the A-phase magnetic field detection element and the B-phase magneticfield detection element are mounted on the rotary disc side of thecircuit board, and

the T-phase magnetic field detection element is mounted on a side of thecircuit board in opposite to the rotary disc side.

EFFECTS OF THE INVENTION

According to the invention claimed in claims 1 and 2, themulti-revolution signal generation portion is configured by a magneticdetection means having a small consumption current, and one of theA-pulse generation portion and the B-pulse generation portion is fed ina pulsation manner at the time of the cut-off of the external powersupply, so that a consumption current can be reduced. Thus, theelongation of the life time of the backup power supply can be realizedand the maintenance. can be simplified. Further, when an MR element isused for the magnetic field detection element, a consumption current canbe further reduced.

According to the invention claimed in claims 3 and 4, themulti-revolution signal generation portion is configured by a magneticdetection means having a small consumption current, and the A-pulsegeneration portion and the B-pulse generation portion are fed in apulsation manner at the time of the cut-off of the external power supplybased on the T pulse of two pulses/revolution, so that a consumptioncurrent can be reduced. Thus, the elongation of the life time of thebackup power supply can be realized and the maintenance can besimplified. Further, when an MR element is used for the T-phase magneticfield detection element, a consumption current can be further reduced.

According to the invention claimed in claim 5, since the magnetic fieldsextending perpendicular to the circuit board and the magnetic fieldsextending in parallel to the circuit board from a magnetizing portionare used as a detection signal, an allowable value of the setting of agap between the circuit board and the rotary disc can be made large.Further, when the elements are selected and disposed on the main andrear surfaces of the circuit board so as to match to the sensitivedirection of the elements, a small-sized absolute multi-revolutionencoder can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS

-   -   FIG. 1 illustrates a block diagram showing the multi-revolution        detection circuit of an absolute multi-revolution encoder        according to the first embodiment of the invention.

FIGS. 2( a) and 2(b) illustrate waveform diagrams at the respectiveportions of the multi-revolution detection circuit in the firstembodiment of the invention (at the time of supplying power from anexternal power supply).

FIGS. 3( a ) and 3(b) illustrate waveform diagrams at the respectiveportions of the multi-revolution detection circuit in the firstembodiment of the invention (at the time of the backup operation).

FIG. 4 illustrates a block diagram showing the multi-revolutiondetection circuit of an absolute multi-revolution encoder according tothe second embodiment of the invention.

FIG. 5 illustrates a side view showing the arrangement of magnetic fielddetection elements according to the second embodiment of the invention.

FIG. 6 illustrates a plan view showing the arrangement of magnetic fielddetection elements according to the second embodiment of the invention.

FIG. 7 illustrates a graph showing the characteristics of an MR elementaccording to the second embodiment of the invention.

FIGS. 8( a) and 8(b) illustrate waveform diagrams at the respectiveportions of the multi-revolution detection circuit in the secondembodiment of the invention (at the time of supplying power from anexternal power supply).

FIGS. 9( a) and 9(b) illustrate waveform diagrams at the respectiveportions of the multi-revolution detection circuit in the secondembodiment of the invention (at the time of the backup operation).

FIG. 10 illustrates a side view showing the mechanical configuration ofan absolute multi-revolution encoder of a related art.

FIG. 11 illustrates a plan view showing the configuration of the rotarydiscs of the absolute multi-revolution encoder of a related art.

EXPLANATION OF REFERENCE NUMERALS

-   1 rotary disc-   11 disc magnet-   12 optical slit-   2 power supply selection switch-   3 multi-revolution signal generation portion-   31 A-pulse generation portion-   310 A-phase magnetic field detection element-   311 A-phase detection portion-   312 A-pulse generation circuit-   32 B-pulse generation portion-   320 B-phase magnetic field detection element-   321 B-phase detection portion-   322 B-pulse generation circuit-   33 counter-   34 T-pulse generation portion-   340 T-phase magnetic field detection element-   341 T-phase detection portion-   342 T-pulse generation circuit-   35 power supply control pulse generation circuit-   36 feeding control portion-   4 within-one-revolution signal generation portion-   5 circuit board

BEST MODES FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments according to the invention will be explainedwith reference to drawings.

First Embodiment

FIG. 1 is a block diagram showing the multi-revolution detection circuitof an absolute multi-revolution encoder according to the firstembodiment of the invention.

In the figure, a reference numeral 1 depicts a rotary disc, 2 a powersupply selection switch, 3 a multi-revolution signal generation portionand 4 a within-one-revolution signal generation portion.

A disc magnet 11, serving as a magnetic material member for generating amulti-revolution signal, is attached to the rotary disc 1. Further,optical slits 12 for generating a within-one-revolution signal is formedat the rotary disc. The disc magnet 11 is formed in a manner that a pairof magnets N, S are directed perpendicular to a rotation shaft. Further,a reference numeral 310 depicts an A-phase magnetic field detectionelement and 320 depicts a B-phase magnetic field detection element.These magnetic field detection elements are disposed to oppose to therotary disc 1 via a gap so as to have an angular difference of 90degrees therebetween. As magnetic field detection element, an MR elementis used as the A-phase magnetic field detection element 310 and a Hallelement is used as the B-phase magnetic field detection element 320.

In the multi-revolution signal generation portion 3, a reference numeral31 depicts an A-pulse generation portion which is constituted by anA-phase detection portion 311 for detecting a signal from the magneticfield detection element 310 and an A-pulse generation circuit 312 forconverting an output from the A-phase detection portion 311 into asignal of a rectangular wave shape (A pulse) . Further, a referencenumeral 32 depicts a B-pulse generation portion which is constituted bya B-phase detection portion 321 for detecting a signal from the magneticfield detection element 320 and a B-pulse generation circuit 322 forconverting an output from the B-phase detection portion 321 into asignal of a rectangular wave shape (B pulse). Further, a referencenumeral 33 depicts a counter for generating a multi-revolution signalfrom the A pulse signal and the B pulse signal. Furthermore, referencenumerals 35 and 36 depict a feeding means for feeding in a pulsationmanner, in which a reference numeral 35 depicts a power supply controlpulse generation circuit for generating a signal with a predeterminedpulse width which starts from the edge of the A pulse signal or the Bpulse signal, and 36 depicts a feeding control portion for feeding in apulsation manner based on the signal from the power supply control pulsegeneration circuit 35.

The first embodiment of the invention differs from the related art inthe following point.

In the relate art, in the case of detecting the multi-revolution in theoff state of the external power supply, a multi-revolution amount isdetected in accordance with the combination of the signals from theoptical means for detecting a within-one-revolution signal by using theLED and the magnetic means for detecting the neighborhood of the originposition in a manner that the LED is fed from the backup power supplyonly for a time period necessary for detecting the multi-revolutionamount, thereby reducing the consumption current. In contrast, in thisembodiment, a multi-revolution amount is detected not by using anoptical means but by counting the A pulse signal and the B pulse signalobtained from a magnetic detection means in a manner that one of theA-pulse generation portion and the B-pulse generation portion is fed ina pulsation manner from the backup power supply only for a time periodnecessary for detecting the multi-revolution amount, thereby reducingthe consumption current.

Next, the operation of the first embodiment of the invention will beexplained.

First, explanation will be made as to the case where power is fed fromthe external power supply.

In FIG. 1, when the rotary disc 1 rotates, the disc magnet 11 rotatestogether with the rotary disc 1. The A-phase detection portion 311 andthe B-phase detection portion 312 detect magnetic fields of the discmagnet 11 by the A-phase magnetic field detection element 310 and theB-phase magnetic field detection element 320 and supply detected signalsto the A-pulse generation circuit 312 and the B-pulse generation circuit322, respectively. The A-pulse generation circuit 312 and the B-pulsegeneration circuit 322 amplify input signals by not-shown amplifiers andconvert the amplified signals by not-shown comparators into the A pulseand the B pulse each being a two-phase rectangular wave signal,respectively. Each of the A pulse and the B pulse is a signal with aduty ratio of 50% and one pulse/one revolution, and the A pulse and theB pulse have a phase difference of 90 degree therebetween.

FIG. 2 is diagrams showing waveforms at the respective portions of themulti-revolution detection circuit in the case of being fed from theexternal power supply in the first embodiment of the invention, andshows the waveforms of the A pulse and the B pulse when the rotary disc1 rotates at a constant speed. FIG. 2( a) shows the waveforms at thetime of the rotation in the forward direction and FIG. 2( b) shows thewaveforms at the time of the rotation in the reverse direction, in whicha depicts the A pulse and b depicts the B pulse. As shown in FIG. 2( a),at the time of the rotation in the forward direction, the B pulse bbecomes an H level upon the rising edge of the A pulse a. In this case,the counter 33 performs the calculation of “multi-revolution amount data+1” to count up the multi-revolution amount data. As shown in FIG. 2(b), at the time of the rotation in the reverse direction, the B pulse bbecomes the H level upon the falling edge of the A pulse a. In thiscase, the counter 33 performs the calculation of “multi-revolutionamount data −1” to count down the multi-revolution amount data. In thismanner, in the case of being fed from the external power supply, thepower is continuously fed to all the circuits of the multi-revolutionsignal generation portion 3 thereby to generate the multi-revolutionsignal.

Next, the explanation will be made as to the backup operation in whichthe external power supply is cut off and the power is fed from thebackup power supply.

In FIG. 1, at the time of the cut-off of the external power supply suchas a power failure, the power supply selection switch 2 is switched tothe backup power supply side in accordance with a power supply switchingsignal e supplied from a not-shown detection circuit when the voltage ofthe external power supply reduces to a predetermined voltage or less.When the power supply is switched to the backup power supply side, thepower is not supplied to the within-one-revolution signal generationportion 4 and the power is supplied only to the multi-revolution signalgeneration portion 3 from the backup power supply. Further, when thepower supply control pulse generation circuit 35 detects the edge of theA pulse, this circuit generates a power supply control pulse d with apredetermined pulse width which is generated so as to start from theedge thereby to restrict the power supply to the B-pulse generationportion 32. That is, although the A-pulse generation portion 31 iscontinuously fed by the backup power supply, the B-pulse generationportion 32 is supplied via the feeding control portion 36 with thepulsation power which is restricted by the power supply control pulse d.

FIG. 3 is diagrams showing waveforms at the respective portions of themulti-revolution detection circuit at the time of the backup operationin the first embodiment of the invention.

FIG. 3( a) shows the waveforms at the time of the rotation in theforward direction and FIG. 3( b) shows the waveforms at the time of therotation in the reverse direction, in which the A pulse a, the B pulse band the power supply control pulse d when the rotary disc 1 rotates at aconstant speed are shown. A TON period during which the power supplycontrol pulse d is at an H level is a period during which the power fromthe backup power supply is supplied to the B-pulse generation portion32. A TOFF period is a period during which the power from the backuppower supply is not supplied to the B-pulse generation portion 32. Thus,the B pulse b is fixed at its level only during the TON period shown bya steady line. when the counter 33 detects the edge of the A pulse a,the counter detects the level of the B pulse b during the TON periodthereby to update the count value thereof. The up and down operation ofthe count value is performed in the similar manner as the case where thepower is fed from the external power supply. That is, at the time of therotation in the forward direction, the B pulse becomes an H level uponthe rising edge of the A pulse. In this case, the counter performs thecalculation of “multi-revolution amount data +1” to count up themulti-revolution amount data. At the time of the rotation in the reversedirection, the B pulse becomes an H level upon the falling edge of the Apulse. In this case, the counter 33 performs the calculation of“multi-revolution amount data −1” to count down the multi-revolutionamount data. The power supply control pulse d may have a pulse widthsufficient for detecting the H/L levels of the B pulse.

In this manner, according to this embodiment, at the time of the backupoperation, the power from the backup power supply is fed only to themulti-revolution signal generation portion 3, whilst the B-pulsegeneration portion 32 is supplied with the power from the backup powersupply only during the predetermined period (TON period) necessary fordetecting the level of the B pulse. Thus, the consumption current at thetime of the backup operation can be reduced. Accordingly, the life timeof the backup power supply can be elongated and the maintenance can besimplified. Further, the cost of the maintenance required for exchangingthe backup power supply such as a battery can be reduced.

Although, in this embodiment, the explanation is made as to an examplein which each of the B-phase detection portion 321 and the portion 322within the B-pulse generation portion 32 is fed in a pulsation manner,either one of the B-phase detection portion 321 and the portion 322 maybe fed in a pulsation manner.

Second Embodiment

FIG. 4 is a block diagram showing the multi-revolution detection circuitof an absolute multi-revolution encoder according to the secondembodiment of the invention. In this embodiment, portions having thesame configurations as those of the first embodiment omitted in theirexplanation and only the portions different from the first embodimentwill be explained.

In FIG. 4, a reference numeral 340 depicts a T-phase magnetic fielddetection element for outputting a signal of two pulses/revolution. Areference numeral 34 depicts a T-pulse generation portion which isconfigured by a T-phase detection portion 341 for detecting the outputfrom the T-phase magnetic field detection element and a T-pulsegeneration circuit 342 for converting an output from the T-phasedetection portion 341 into a signal of a rectangular wave shape(T-pulse).

FIG. 5 is a side view showing the arrangement of the magnetic fielddetection elements according to the second embodiment of the inventionand FIG. 6 is a plan view thereof.

In these figures, a reference numeral 5 depicts a circuit board. TheA-phase magnetic field detection element 310 and the B-phase magneticfield detection element 320 are disposed on the surface of the circuitboard 5 on the rotary disc 1 side, whilst the T-phase magnetic fielddetection element 340 are disposed on the surface of the circuit board 5in opposite to the rotary disc 1 side. A reference numeral 6 depictsmagnetic field lines, which represent a state of the magnetic fieldswhen magnetic poles are disposed at the left and right sides in thefigure, respectively. The magnetic field extending in the directionperpendicular to the circuit board 5 interlinks with the A-phasemagnetic field detection element 310 and the B-phase magnetic fielddetection element 320, whilst the magnetic field extending in parallelto the circuit board 5 interlinks with the T-phase magnetic fielddetection element 340.

In this embodiment, the Hall element having the detection sensitivitywith respect to the magnetic field extending in the directionperpendicular to the circuit board 5 is used for each of the A-phasemagnetic field detection element 310 and the B-phase magnetic fielddetection element 320, whilst the MR element having the detectionsensitivity with respect to the magnetic field extending in parallel tothe circuit board 5 is used for the T-phase magnetic field detectionelement 340.

This embodiment differs from the first embodiment in the followingpoint.

In the first embodiment, the consumption current is reduced in a mannerthat the power from the backup power supply is supplied in a pulsationmanner to one of the A-pulse generation portion and the B-pulsegeneration portion only during the time period necessary for detecting amulti-revolution amount. In contrast, in this embodiment, theconsumption current is reduced in a manner that the T-phase magneticfield detection element 340 for outputting the signal of twopulses/revolution is disposed on the circuit board, the T pulse signalfor controlling the supply of the power is generated based on the signalobtained from the T-phase magnetic field detection element 340, and thepower from the backup power supply is supplied in a pulsation manner tothe A-pulse generation portion 31 and the B-pulse generation portion 32only during the time period necessary for detecting a multi-revolutionamount from the time point starting from the edge of the T pulse.

Next, the operation of the second embodiment of the invention will beexplained.

FIG. 7 is a graph showing the characteristics of the MR element used asthe T-phase magnetic field detection element 340. The resistance valueof the element changes cyclically twice each time the rotary disc 1rotates by one revolution. The T-phase detection portion 341 shown inFIG. 4 detects this resistance change and supplies a detection signal tothe T-pulse generation circuit 342. The T-pulse generation circuit 342amplifies the input signal by a not-shown amplifier and converts theamplified signal by a not-shown comparator into the T pulse. The T pulseis the signal of two pulses/one revolution.

First, the explanation will be made as to the operation of themulti-revolution signal generation portion 3 in the case where the poweris supplied from the external power supply.

FIG. 8 is diagrams showing waveforms at the respective portions of themulti-revolution detection circuit in the second embodiment of theinvention. FIG. 8( a) shows the waveforms at the time of the rotation inthe forward direction and FIG. 8( b) shows the waveforms at the time ofthe rotation in the reverse direction, in which a depicts the A pulse, bdepicts the B pulse and c depicts the T pulse.

At the time of the rotation in the forward direction as shown in FIG. 8(a), upon the falling edge of the T pulse c, there arises a state (Δpoint) that the A pulse a is at an L level and the B pulse b is at an Hlevel. Under this condition, the counter 33 performs the calculation of“multi-revolution amount data +1” to count up the multi-revolutionamount data. As shown in FIG. 7( b), at the time of the rotation in thereverse direction, upon the rising edge of the T pulse c, there arises astate (Δ point) that the A pulse a is at the L level and the B pulse bis at the H level. Under this condition, the counter 33 performs thecalculation of “multi-revolution amount data −1” to count down themulti-revolution amount data.

Next, the explanation will be made as to the operation of themulti-revolution signal generation portion 3 at the time of the backupoperation.

In FIG. 4, when the power supply is switched to the backup power supplyside at the time of the cut-off of the external power supply such as apower failure, the power is not supplied to the within-one-revolutionsignal generation portion 4 and the power from the backup power supplyis applied only to the multi-revolution signal generation portion 3.Further, the power is supplied in a pulsation manner from the backuppower supply to the A-pulse generation portion 31 and the B-pulsegeneration portion 32. That is, the power supply control pulsegeneration circuit 34 generates the power supply control pulse d withthe predetermined pulse width which is generated so as to start from theedge of the T pulse c. Then, the feeding control portion 36 supplies,based on the power supply control pulse d, the power from the backuppower supply to the A-pulse generation portion 31 and the B-pulsegeneration portion 32 only during the period that the power supplycontrol pulse d is at the H level.

FIG. 9 is diagrams showing waveforms at the respective portions of themulti-revolution detection circuit at the time of the backup operationin the second embodiment of the invention.

FIG. 9( a) shows the waveforms at the time of the rotation in theforward direction and FIG. 9( b) shows the waveforms at the time of therotation in the reverse direction, in which a depicts the A pulse, bdepicts the B pulse, c depicts the T pulse and d depicts the powersupply control pulse. A TON period represents a time period during whichthe power from the backup power supply is supplied to the A-pulsegeneration portion 31 and the B-pulse generation portion 32, whilst aTOFF period represents a time period during which the power is notsupplied. Thus, the A pulse a and the B pulse b are fixed at theirlevels only during the TON period shown by steady lines.

The counter 33 detects the edge of the T pulse during the TON period andthen detects the levels of the A pulse a and the B pulse b during theTON period thereby to increment or decrement the count value thereof.The counting operation of the counter 33 is same as the case where thepower is supplied from the external power supply. That is, at the timeof the rotation in the forward direction, upon the falling edge of the Tpulse c, there arises a state (Δ point) that the A pulse is at an Llevel and the B pulse is at an H level. Then, the counter 33 performsthe calculation of “multi-revolution amount data +1”. At the time of therotation in the reverse direction, upon the rising edge of the T pulsec, there arises a state (Δ point) that the A pulse a is at the L leveland the B pulse bis at the H level. Then, the counter 33 performs thecalculation of “multi-revolution amount data −1”. The count value is notchanged in each of the conditions other than the aforesaid conditions asto the A pulse and the B pulse at the edge of the T pulse.

In this manner, according to this embodiment, at the time of the backupoperation, the power from the backup power supply is fed only to themulti-revolution signal generation portion 3, whilst the A-pulsegeneration portion 31 and the B-pulse generation portion 32 are suppliedwith the power from the backup power supply only during thepredetermined period of the TON period necessary for detecting thelevels of the A pulse and the B pulse and not supplied with the powerduring the TOFF time period. Thus, the consumption current of the backuppower supply can be reduced. Accordingly, the life time of the backuppower supply can be elongated and the maintenance can be simplified.Further, the cost of the maintenance required for exchanging the backuppower supply such as a battery can be reduced.

Further, the Hall elements and the MR element are used for the detectionof the multi-revolution signal and these elements are disposed so as todetect the magnetic fields extending in the direction perpendicular tothe circuit board and the magnetic fields extending in parallel to thecircuit board. Thus, the degree of freedom of the setting of the gapbetween the rotary disc and the Hall elements disposed so as to opposeto each other in the axial direction, that is, the circuit board can bemade large. Thus, the setting of the gap can be optimized on the opticaldetection means side for generating the within-one-revolution signal.

Although, in this embodiment, the explanation is made as to an examplein which each of the A-pulse generation portion 31 and the B-pulsegeneration portion 32 is fed in a pulsation manner, the A-phasedetection portion 311, the B-phase detection portion 321 or the portion312, the portion 322 may be fed in a pulsation manner.

INDUSTRIAL APPLICABILITY

In this manner, according to the invention, since the consumptioncurrent can be reduced to a large extent as compared with the method ofthe related art, the life time of the backup power supply can beelongated. Thus, a product, on which an absolute multi-revolutionencoder employing the system of the invention is mounted, can be usedcontinuously for a long time. Thus, the invention can be applied toindustrial machines which are used in plant systems or production linesystems that are required to be operated continuously for a long term.

1. An absolute multi-revolution encoder comprising: a rotary disc; amulti-revolution signal generation portion; and a within-one-revolutionsignal generation portion, wherein the rotary disc includes a magneticmaterial member which generates a multi-revolution signal, and themulti-revolution signal generation portion includes an A-phase magneticfield detection element and a B-phase magnetic field detection elementwhich detect leakage fluxes of the magnetic material member and outputsignals of one pulse/revolution having phases different by 90 degreesthere between, an A-pulse generation portion including an A-phasedetection portion which detects a signal from the A-phase, magneticfield detection element and an A-pulse generation circuit which convertsthe detected signal into an A pulse of a rectangular wave shape, aB-pulse generation portion including a B-phase detection portion whichdetects a signal from the B-phase magnetic field detection element andan B-pulse generation circuit which converts the detected signal into aB pulse of a rectangular wave shape, a counter which counts the A pulseand the B pulse to generate the multi-revolution signal, and a powersupply means which supplies power from a backup power supply for adetermined time period to at least one of the B-phase detection portionand the B-pulse generation circuit based on the A pulse or to at leastone of the A-phase detection portion and the A-pulse generation circuitbased on the B pulse.
 2. The absolute multi-revolution encoder accordingto claim 1, wherein at least one of the A-phase magnetic field detectionelement and the B-phase magnetic field detection element is an MRelement.
 3. An absolute multi-revolution encoder comprising: a rotarydisc; a multi-revolution signal generation portion; and awithin-one-revolution signal generation portion, wherein the rotary discincludes a magnetic material member which generates a multi-revolutionsignal, the magnetic material member is formed of a permanent magneticwhich is magnetized along a direction perpendicular to a rotation axisof the rotary disc, and the multi-revolution signal generation portionincludes: an A-phase magnetic field detection element and a B-phasemagnetic field detection element which detect leakage fluxes of themagnetic material member and output signals of one pulse/revolutionhaving phases different by 90 degrees there between, an A-pulsegeneration portion including an A-phase detection portion which detectsa signal from the A-phase magnetic field detection element and anA-pulse generation circuit which converts the detected signal into an Apulse of a rectangular wave shape, a B-pulse generation portionincluding a B-phase detection portion which detects a signal from theB-phase magnetic field detection element and an B-pulse generationcircuit which converts the detected signal into a B-pulse of arectangular wave shape, a counter which counts the A pulse and theB-pulse: to generate the multi-revolution signal, a T-phase magneticfield detection element which detects leakage fluxes of the magneticmaterial member and outputs a signal of two pulses/revolution, a T-pulsegeneration portion including a T-phase detection portion which detects asignal from the T-phase magnetic field detection element and a T-pulsegeneration circuit which converts the detected signal into a T pulse ofa rectangular wave shape, and a power supply means which supplies powerfrom a backup power supply for a predetermine time period based on the Tpulse to one of a following cases: a) both of the A-phase detectioncircuit and the B-phase detection circuit, b) both of the A-pulsegeneration circuit and the B-pulse generation circuit, and c) all of theA-phase detection circuit, the B-phase detection circuit, A-pulsegeneration circuit and B-pulse generation circuit.
 4. The absolutemulti-revolution encoder according to claim 3, wherein each of theA-phase magnetic field detection element and the B-pulse magnetic fielddetection element is a Hall element, and the T-phase magnetic fielddetection element is an MR element.
 5. The absolute multi-revolutionencoder according to claim 3, wherein a circuit board is disposed inparallel to the rotary disc via a gap, the A-phase magnetic fielddetection element and the B-phase magnetic field detection element aremounted on the rotary disc side of the circuit board, and the T-phasemagnetic field detection element is mounted on a side of the circuitboard in opposite to the rotary disc side.